A friend of mine had great fun going in to buy a car carrying a briefcase. She negotiated her deal on the car, and then when they tried to set up financing, she told them she wanted to pay for the car up front. In cash. Actual cash. The briefcase was full of it. 
She told us later she had been tempted to point out that they were "non-consecutive bills" but thought that might be pushing it. They did not know what to do, and ended up calling in several extra car salesman to help count the money (she'd had it organized, of course, but they had to verify).
My dad did that once. They had to give him $40.57 in change--but they didn't have any change, because no one ever buys a car for cash. They had to ask him if he would take a check for what they owed him.
The salesman was pretty darned surprised at getting cash. I think he was also worried about whether he could get it all to the bank before it close
Paying for a car completely in cash can also be the sign of criminal activity and may raise suspicions.
Before my beloved dad passed away, he worked as a stock checker and auditor for a luxury car dealership in an expensive part of inner city Sydney. This dealership was a highly exclusive dealership- no Toyotas, Suzukis or Holdens, Ashton Martins, Bentleys, Rolls Royces, Jaguars. In fact, a certain ex-WAG had her very infamous car purchased from this dealership and was a frequent customer. I digress, but the point is, this was not a dealership that sold cheap cars. In fact, many of them cost over the million dollar mark (Dad to Me: "Kat, you know you're leaning on $1.5 million?")
Anyway, one day whilst my dad was doing his rounds a young Asian man (yes his race is important) and his girlfriend came in and wanted to buy a Bentley SUV (don't quote me), which was around the $200 000. This is all well and good, nothing wrong here, except that the man wanted to pay completely in cash. Oh, and he had a $20 000 cash deposit with in in the sports bag he was holding.
In addition, because the man was wearing a singlet/wife beater, his arms and back were fairly exposed, all of which were completely tattooed in well known Hong Kong/Chinese gang symbols, most prominent of which was a huge dragon. Naturally, the dealership declined the would be customers' sale, informing him that legally they could not accept that amount of cash. They then the gang squad at the local police station, who confirmed the dealerships suspicions after they described the tattoos.
This wasn't the first time it happened either, nor was it limited to just Asian gangs- I believed that the Legitimate Businessman's Social Club was also a big fan of luxury cars. But it makes sense- if you've got a heap of cash from illegal activities, one of the best ways to 'legitimise' this money is by buying cars, especially at the higher end dealerships where pleasing the customer is paramount. That being said, it is mandatory for any large vash purchases to be reported to police, or they run the risk of being found complicit in money laundering and organised crime. That's why a lot of dealerships don't keep money or make change.
Just thought I'd show the other side of the cash for cars debate!
